The present invention relates to an aberration corrector and an electron microscope.
In electron microscopes such as a transmission electron microscope (TEM) and a scanning electron microscope (SEM), spherical aberration and chromatic aberration are one of the causes of resolution degradation.
In recent years, spherical aberration correctors have been put to practical use. For example, JP-A-2009-54565 discloses a spherical aberration corrector capable of removing a higher-order aberration while correcting a spherical aberration using three-fold symmetric fields (magnetic fields having three-fold symmetry or electric fields having three-fold symmetry) in three stages.
As more and more spherical aberration correctors are being put to practical use, the development of chromatic aberration correctors is next expected. For example, JP-A-2014-116219 discloses an optical system which corrects a chromatic aberration using superimposed electromagnetic two-fold fields (electromagnetic fields having two-fold symmetry formed by a superposition of an electric field having two-fold symmetry and a magnetic field having two-fold symmetry) in two stages. While the chromatic aberration corrector described in JP-A-2014-116219 adopts superimposed electromagnetic two-fold fields in two stages generated by multipole elements in two stages as a basic configuration, an orbit resembling that of a concave-convex-concave lens is realized by dividing a single multipole element into three portions.
In addition, F. Hosokawa, H. Sawada, Y. Kondo, K. Takayanagi and K. Suenaga, Microscopy 62(1): 23-41 (2013) discloses a result of an experiment of simultaneously correcting a chromatic aberration and a spherical aberration using an apparatus constituted by a spherical aberration corrector and a chromatic aberration corrector connected in tandem.
Connecting a spherical aberration corrector and a chromatic aberration corrector in tandem as described in F. Hosokawa, H. Sawada, Y. Kondo, K. Takayanagi and K. Suenaga, Microscopy 62(1): 23-41 (2013) increases a length along an optical axis and results in a greater overall length of an electron microscope. As a result, for example, a problem in that a height requirement for a room in which the electron microscope is to be installed increases or a problem in that stability of the electron microscope declines may occur.